[pypy-commit] stmgc c8-tcp-style-trx-length: Implement TCP style linear transaction length increase after abort, exponential increase only initially or after a constant amount of transactions

[tobweber]

Author: Tobias Weber <tobias_weber89 at gmx.de>
Branch: c8-tcp-style-trx-length
Changeset: r2078:91207e4ad1b8
Date: 2017-06-26 12:22 +0200
http://bitbucket.org/pypy/stmgc/changeset/91207e4ad1b8/

Log:	Implement TCP style linear transaction length increase after abort,
	exponential increase only initially or after a constant amount of
	transactions

diff --git a/c8/stm/nursery.c b/c8/stm/nursery.c
--- a/c8/stm/nursery.c
+++ b/c8/stm/nursery.c
@@ -21,26 +21,32 @@
 #define LARGE_FILL_MARK_NURSERY_BYTES   0x1000000000L
 // #define LARGE_FILL_MARK_NURSERY_BYTES   0x1000000000000000L
 
-#define STM_MIN_RELATIVE_TRANSACTION_LENGTH (0.00000001)
+// corresponds to ~7 bytes nursery fill
+#define STM_MIN_RELATIVE_TRANSACTION_LENGTH (0.0000000001)
 
 static double get_new_transaction_length(stm_thread_local_t *tl, bool aborts) {
     const int multiplier = 100;
     double previous = tl->relative_transaction_length;
     double new = previous;
     if (aborts) {
-        tl->transaction_length_backoff = 3;
         if (previous > STM_MIN_RELATIVE_TRANSACTION_LENGTH) {
             new = previous / multiplier;
         } else {
-            new = 0;
+            new = STM_MIN_RELATIVE_TRANSACTION_LENGTH;
         }
+        // the shorter the trx, the more backoff
+        tl->transaction_length_backoff = (int)(1 / new);
+        tl->linear_transaction_length_increment = new;
     } else if (tl->transaction_length_backoff == 0) {
-        if (previous - (STM_MIN_RELATIVE_TRANSACTION_LENGTH * 0.1) < 0) {
-            new = STM_MIN_RELATIVE_TRANSACTION_LENGTH;
-        } else if (previous < 1) {
+        // backoff counter is zero, exponential increase up to 1
+        if (previous < 1) {
             new = previous * multiplier;
         }
     } else { // not abort and backoff != 0
+        // in backoff, linear increase up to 1
+        if (previous < 1) {
+            new = previous + tl->linear_transaction_length_increment;
+        }
         tl->transaction_length_backoff -= 1;
     }
     return new;
diff --git a/c8/stm/setup.c b/c8/stm/setup.c
--- a/c8/stm/setup.c
+++ b/c8/stm/setup.c
@@ -246,9 +246,10 @@
     tl->last_associated_segment_num = num + 1;
     tl->thread_local_counter = ++thread_local_counters;
 
-    /* init single thread mode */
+    /* init adaptive transaction length mode */
     tl->relative_transaction_length = STM_MIN_RELATIVE_TRANSACTION_LENGTH;
     tl->transaction_length_backoff = 0;
+    tl->linear_transaction_length_increment = 0;
 
     *_get_cpth(tl) = pthread_self();
     _init_shadow_stack(tl);
diff --git a/c8/stmgc.h b/c8/stmgc.h
--- a/c8/stmgc.h
+++ b/c8/stmgc.h
@@ -92,8 +92,10 @@
     /* == adaptive single thread mode == */
     /* factor that is multiplied with max transaction length before the start of the next transaction on this thread */
     double relative_transaction_length;
-    /* when zero, transaction length may increase or decrease, otherwise transaction length may only decrease. is (re-)set to some value upon abort and counted down until zero upon successful validation. */
+    /* when zero, transaction length may increase exponentially, otherwise transaction length may only increase linearly. is (re-)set to some value upon abort and counted down until zero upon successful validation. */
     int transaction_length_backoff;
+    /* during the backoff, transaction length may increase linearly by this increment on every successful validation */
+    double linear_transaction_length_increment;
 } stm_thread_local_t;